Apparatus for molding a plastic closure with air-assisted ejection

ABSTRACT

An apparatus for molding a plastic closure includes a male mold assembly including a forming pin and an outer pin sleeve which cooperate with a female mold for defining a mold cavity. To facilitate mechanical stripping of a molded closure from the forming pin, pressurized air is introduced into the molded closure through at least one air passageway which extends axially between the forming pin and pin sleeve. By outwardly expanding and forming the plastic closure during ejection from the forming pin, forces to which the closure is subjected during ejection are significantly reduced, thereby desirably reducing the amount of cooling of the closure that is required during the molding cycle prior to ejection. Significantly increased operating speeds for the compression molding apparatus can thus be achieved.

TECHNICAL FIELD

The present invention relates generally to an apparatus and method forcompression molding a plastic closure, and more particularly to anapparatus and method for effecting air-assisted ejection of a moldedclosure from associated mold tooling, thereby facilitating high-speedclosure manufacture while avoiding unacceptable closure deformation.

BACKGROUND OF THE INVENTION

Compression molded plastic closures have found very widespreadacceptance in the marketplace, with such closures being particularlysuited for use on carbonated beverages, as well as other applicationsrequiring the desirable strength and sealing characteristics which suchclosures can provide. Additionally, these types of closures can bereadily configured to provide tamper-indication, thus assuring consumersof the desired product quality.

U.S. Pat. No. 4,378,893, No. 4,407,422, No. 4,418,828, and No.4,978,017, all hereby incorporated by reference, illustrate plasticclosure constructions, including closures which can be configured fortamper-indication, which can be efficiently and economically formed bycompression molding. U.S. Pat. No. 4,343,754, No. 4,497,765, No.5,554,327, No. 5,670,100, and No. 5,866,177, all hereby incorporated byreference, disclose methods and apparatus by which plastic closures canbe formed by compression molding.

For typical applications, a compression molded closure includes aretention element, typically in the form of a helical thread formation,on an inside surface of a skirt portion of the closure. A male mold ofthe compression molding tooling, sometimes referred to as a forming pin,includes an outer mold surface which is suitably configured forformation of the closure thread formation. In order to facilitatehigh-speed manufacture of such closures, it has typically been thepractice to mechanically “strip” the molded plastic closure from theforming pin, without any relative rotation for “unthreading” the closurefrom the forming pin. Mechanical stripping of the interference fitbetween the molded closure and the forming pin requires that the skirtportion of the closure be outwardly deformed as the closure threads areurged out of the grooves or other features of the forming pin withinwhich they are molded.

Experience has shown that deformation of the thread formation which canoccur attendant to this stripping action generally acts to limit thespeeds with which plastic closures can be formed. While typical rotarycompression molding machines include water cooling passages within themold tooling components, operational speeds are typically limited by thetime required for the molded thread formation to become sufficientlysolid as to permit the mechanical stripping of each closure from itsrespective forming pin, without unacceptable deformation of the threadformation or other portions of the closure.

Heretofore, efforts have been made to facilitate this mechanicalstripping of a threaded plastic closure from an associated male moldtooling. Use of compressed gas, directed into a molded plastic closureduring removal from associated tooling, has been practiced in connectionwith injection molding of closures. Efforts have also been made toincorporate such air-ejection arrangements in compression moldingequipment, such as exemplified by U.S. Pat. No. 5,786,079, herebyincorporated by reference, and published PCT patent application No. WO01/32390, hereby incorporated by reference. However, these previouslyknown arrangements have undesirably increased the complexity of tooling,and in one construction, required the provision of an air passage whichgenerally tends to reduce the sizes of coolant passages within thetooling. Such arrangements have also been generally limited in the sizeof passageways provided for direction of air into a molded closure, andhave been configured in a way which can undesirably result in thin metalportions of tooling, detracting from durability.

The present invention is directed to an improved apparatus forcompression molding of plastic closures, and method of operation, whichfacilitates high-speed closure manufacture by introduction of compressedgas, air, typically into a molded closure during its removal from anassociated male mold forming pin, with the system desirably configuredto maintain the integrity of the associated tooling, and permittingcost-effective use in compression molding equipment.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus for molding a plasticclosure, and method of operation, which facilitates high-speed closuremanufacture by introduction of compressed gas (air) into a moldedplastic closure during that portion of the molding cycle in which theplastic closure is mechanically “stripped” from an associated male moldforming pin. In the illustrated embodiment, wherein the apparatus isconfigured for molding a plastic closure including a retention element,typically in the form of a helical thread formation for securing theclosure on an associated container, the apparatus is configured in amanner which directs pressurized air into the closure in a regionbetween the retention element and a free edge of the closure. This hasbeen found to desirably create forces on the interior of the closure,particularly in the region of the retention element (thread formation)which greatly facilitate high-speed removal of the closure from theassociated male forming pin.

Notably, incorporation of the air-ejection system into compressionmolding tooling is facilitated by directing the air into the moldedclosure in one or more passageways formed between the male forming pinand an associated outer pin sleeve. Passages having the desired flowarea can be readily formed, while maintaining the integrity of the moldtooling, and without requiring any significant reduction in the sizeand/or number of coolant passages which typically are provided in thecompression molding tooling to facilitate solidification of moltenplastic after it is compression molded.

In accordance with the illustrated embodiment, an apparatus for moldinga plastic closure comprises a male mold assembly including a centralforming pin, and an outer pin sleeve within which the forming pin ispositioned. The apparatus further includes a female mold whichcooperates with the male mold to define a generally cup-shaped moldcavity to form the plastic closure with a top wall portion, and anannular skirt portion. The male mold assembly and female mold arerelatively movable to open the mold cavity for removal of the moldedplastic closure from a free end of the central forming pin.

In the illustrated embodiment, the male mold assembly includes anejection sleeve positioned about the outer pin sleeve, with the formingpin and ejection sleeve being relatively movable so that engagement ofthe ejection sleeve with the skirt portion of the molded plastic closuremoves the plastic closure off of the forming pin. When the plasticclosure is formed with a retention element, such as in the form of ahelical thread formation, on the inside surface of the skirt portion,the action of the ejection sleeve acts to “strip” the molded plasticclosure from the central forming pin by dislodging the closure threadformation from the forming pin.

The male mold assembly defines at least one air passageway which extendsaxially between the central forming pin and the outer pin sleeve. Theair passageway can be placed in fluid communication with the mold cavityto permit pressurized air to be directed into the molded plastic closureafter removal from the female mold, to thereby facilitate removal of theclosure from the central forming pin. Notably, the apparatus isconfigured such that the air passageway communicates with the moldcavity at a region between the retention element of the molded closure,and a surface of the closure, typically a free edge of the skirtportion, which sealingly engages the ejection sleeve. By thisarrangement, the molded closure is sealed against the ejection sleeve aspressurized air is directed into the closure. The closure expandsoutwardly in a balloon-like fashion, thereby facilitating mechanicalstripping of the closure from the central forming pin, including removalof the closure thread formation from the exterior surface of the formingpin within which the thread formation is molded.

In accordance with the preferred embodiment, the central forming pin andouter pin sleeve are relatively movable, and define an annular formingsurface therebetween adjacent a free edge of the skirt portion of theplastic closure. In a typical configuration, the skirt portion of theplastic closure includes at least one tamper-indicating element, whichelement is formed against the annular forming surface of the centralforming pin. Notably, this same interface between the outer pin sleeveand the central forming pin acts to provide a valve-like mechanism whichcontrols and throttles the pressurized air being directed into themolded plastic closure, with pressurized air thus being directed intothe plastic closure during the ejection portion of the molding cycle.

Preferred features of the present apparatus facilitate efficient,high-speed operation while avoiding undesirable deterioration of themold tooling. In the preferred form, a plurality of air passagewaysextend axially between the central forming pin and outer pin sleeve ofthe male mold assembly, with one or more circumferential channelsprovided extending between the forming pin and pin sleeve, joining theplurality of air passageways in fluid communication. In the illustratedembodiment, a pair of circumferential channels are provided joining theplurality of axial air passageways, with an upper one of the channelsacting to distribute air among the air passageways, and with a lower oneof the circumferential channels desirably acting as an accumulator forthe compressed air. In the preferred form, the plurality of axial airpassageways are arranged so as to balance reactive forces created by airpressure between the central forming pin and outer pin sleeve, thusavoiding undesirable binding or wear of the mold tooling, which canotherwise result from an imbalance created within the tooling bydelivery of compressed air between the forming pin and pin sleeve.

By the outward deformation or bulging of the skirt portion of the moldedplastic closure, the force required for mechanically stripping theplastic closure from the forming pin is desirably reduced. This resultsin less closure deformation, which can otherwise be exhibited by bulgedportions of the closure, particularly in the region of thetamper-indicating feature, as well as in the form of deformed threads.

Other features and advantages of the present invention will becomereadily apparent from the following detailed description, theaccompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an apparatus for molding a plasticclosure embodying the principles of the present invention;

FIG. 2 is a relatively enlarged, fragmentary view of the apparatusillustrated in FIG. 1, with a forming pin of the apparatus not shown;

FIG. 3 is a diagrammatic, cross-sectional view of the apparatus shown inFIG. 1, taken generally along lines 3—3 of FIG. 1;

FIG. 4 is a relatively enlarged, diagrammatic view of the apparatusillustrated in FIG. 1, illustrating the apparatus in a closedconfiguration for molding a plastic closure therein;

FIG. 5 is a view similar to FIG. 4 illustrating the present apparatus inan open condition, with removal of a molded plastic closure from anassociated forming pin being initiated;

FIG. 6 is a view similar to FIG. 5 further illustrating removal of themolded plastic closure from the associated forming pin, with the closurehaving been sealed against an associated ejection sleeve, andpressurized air introduced therein;

FIG. 7 is a view similar to FIG. 6 further illustrating removal of themolded plastic closure from the associated forming pin diagrammaticallyillustrating air pressure forces acting against the interior surfaces ofthe illustrated plastic closure for facilitating its removal from theassociated forming pin; and

FIG. 8 diagrammatically illustrates the completion of removal of themolded plastic closure from the forming pin of the associated tooling.

DETAILED DESCRIPTION

While the present invention is susceptible of embodiment in variousforms, there is shown in the drawings, and will hereinafter bedescribed, a presently preferred embodiment, with the understanding thatthe present disclosure is to be considered as an exemplification of theinvention, and is not intended to limit the invention to the specificembodiment illustrated.

The present invention is directed to a compression molding apparatus,and method of operation, which facilitates high-speed manufacture ofmolded plastic closures or like articles by the introduction ofpressurized air into the molded closure during ejection of the closurefrom the associated tooling. In a typical compression molding apparatus,a rotary or turret compression molding machine includes a plurality ofmold tooling assemblies which are configured for operation attendant torotary movement of the compression molder. Each tooling assembly ismoved relative to a suitable extruder or like device, and associatedmetering mechanism, which deposits a predetermined quantity of moltenplastic material into each of the mold assemblies when the assembly isin an opened condition. Continued rotary motion of the apparatus effectsclosing of each mold assembly, typically by cam-actuation, whereby thequantity of molten material is compressed between a male forming pin anda female mold cavity, to thus form a molded plastic closure. The moldtooling is typically provided with internal coolant passages throughwhich coolant is circulated as the compression molder rotates in orderto quickly solidify the molten plastic into the desired cup-like moldedplastic closure.

After the plastic closure is molded, and solidified sufficiently as topermit its removal from the mold tooling, the mold tooling is opened topermit closure removal. Typically, a male mold assembly and associatedfemale mold are relatively moved, thereby exposing the molded closure,as it remains in position on the male mold assembly. Because the plasticclosure is typically formed with a top wall portion, a depending annularskirt portion, and at least one retention element, typically a helicalthread formation on the inside surface of the closure skirt, the closureis retained on the male mold tooling by what is, in essence, aninterference fit, as the thread formation is retained within thatportion of the male mold tooling in which it is formed.

While it is known to effect closure removal by “unthreading” the moldedclosure from the male tooling, high speed manufacture is facilitated bymechanically stripping the closure from the tooling. This is ordinarilyeffected by relatively moving that portion of the male mold, whichretains the closure, relative to an associated ejection or strippersleeve which engages the free edge of the closure skirt. Axial forcesthus created on the skirt portion result in the outward deformation ofthe skirt portion as the closure thread formation moves out of theregion of the male tool in which it is formed. Because the threadformation, by virtue of its cross-sectional area, is typically one ofthe last portions of the closure to fully solidify, operating speed ofthe molding apparatus is typically limited by the time required tosolidify the thread formation sufficiently as to avoid its unacceptabledeformation as the closure is mechanically stripped from the maletooling.

The present invention is directed to a compression molding apparatus,including a male mold assembly, which is specifically configured tofacilitate high-speed manufacture by the direction of pressurized airinto the molded plastic closure during the ejection portion of themolding cycle. Significantly, because the present invention desirablyacts to reduce the forces to which the closure thread formation issubjected during ejection, operating speeds for the molding apparatuscan be very dramatically increased, thus greatly facilitatingmanufacturing efficiency. As will be appreciated, such increased formingspeeds are a direct result of the reduced stresses to which the closurethread formation is subjected, thus permitting higher operating speedswithout unacceptable closure deformation.

With reference now to the drawings, therein is illustrated a plasticclosure mold tooling assembly 10 embodying the principles of the presentinvention. As will be recognized by those familiar with the art, moldtooling assembly 10 is configured for effecting compression molding ofplastic material within a mold cavity defined thereby, as will befurther described. The mold tooling assembly is typically one ofnumerous tools mounted on a rotary or turret compression moldingapparatus, with driven rotation of the apparatus cycling each toolingassembly through the necessary stages for plastic closure manufacture.As is known in the art, mold tooling assembly 10 typically includesinternal coolant passages (not shown) to facilitate solidification of amolded plastic closure, so as to create sufficient column strength inthe closure sidewall or skirt portion to permit stripping of the closurefrom the mold tooling, thus promoting high-speed production.

As illustrated, the mold tooling assembly 10 includes a male moldassembly 12 including a central forming pin 14, and an outer pin sleeve16 within which the forming pin is positioned. The male mold assemblyfurther includes an ejection sleeve 18 positioned about the outer pinsleeve 16, with the forming pin 14 and ejection sleeve 18 beingrelatively movable so that engagement of the ejection sleeve with theskirt portion of a molded plastic closure moves the plastic closure offof the forming pin. Ejection in this manner will be further describedhereinafter.

The mold tooling assembly 10 further includes a female mold whichcooperates with the male mold assembly 12 to define a mold cavity 22 toform a plastic closure. A plastic closure, designated C, isdiagrammatically illustrated in the drawings, and includes a top wallportion W, and an annular skirt portion or side wall S. The annularskirt portion S includes at least one retention element on the insidesurface thereof for securing the closure on an associated container. Theretention element typically comprises a thread formation, designated T,but it will be understood that this specific configuration of theretention element may be varied while keeping with the principlesdisclosed herein.

The mold tooling assembly 10 is carried by the associated rotarycompression molder by a clevis 24. A pin sleeve retainer 26 ispositioned generally beneath the clevis 24 adjacent to the outer pinsleeve 16 of the tooling assembly. Operation of the tooling assembly istypically effected by suitable cams which act to relatively move thevarious components of the tooling for closing the mold cavity after apredetermined quantity of molten plastic material is received therein.Actuation of the tooling effects compression molding of the plastic toform the plastic closure in the mold cavity, with the tooling thereafteropened to facilitate removal of the molded closure, in particular,removal of the molded closure from the plunger-like end of the centralforming pin 14. Forces for compression molding of the plastic aretypically directed through the clevis 24, the pin sleeve 16, the formingpin 14, and the female mold 20.

In accordance with the present invention, the present molding apparatusis configured to direct pressurized gas, air, typically into the moldedplastic closure to facilitate its removal from the central forming pin14. To this end, an air delivery arrangement is provided for directingpressurized air into a plastic closure formed within the mold cavity 22.While use of air as the pressurized gas for the practice of thisinvention is presently preferred, it will be understood that a suitablegas other than air can be employed for practice of the presentinvention. Thus, it is to be understood that use of the term “air”herein with reference to the gas which is pressurized to facilitateclosure ejection is intended to encompass other suitable gasses.

As illustrated in FIGS. 1 and 2, the air delivery arrangement includes acoupling 28 mounted in clevis 24, with the coupling communicating withan internal passage 30 defined by the clevis. Pressurized air directedthrough the coupling 28 into the passage 30 is delivered to the moldtooling assembly from an associated rotary union, which provides avalve-like action to direct pressurized air into the tooling assemblyduring that portion of the molding cycle in which ejection of the moldedclosure is effected. While use of a rotary union (not shown) ispresently preferred, it will be recognized by those skilled in the artthat other valving arrangements, such as suitable electromechanicalvalves or the like, may alternatively be employed for portingpressurized air to the tooling during the appropriate portion of themolding cycle.

The passage 30 of the clevis 24 is in fluid communication with a passage32 defined by pin sleeve retainer 26, with the passage 32 in turncommunicating with a port defined by pin sleeve 16, and an axial airpassageway 34 defined between forming pin 14 and outer pin sleeve 16.While the present invention contemplates that at least one airpassageway 34 be provided between the forming pin 14 and pin sleeve 16,it is presently preferred that a plurality of air passages be providedextending axially between the forming pin and outer pin sleeve. Thepresently preferred arrangement of such air passages is illustrated inFIG. 3, which illustrates, in cross-section, the forming pin 14 and theouter sleeve 16. The preferred provision of a plurality of airpassageways arranged to balance forces exerted on the forming pin avoidsundesirable binding and wear of the tooling components. In theillustrated arrangement, the tooling is provided with the aforesaid airpassageway 34, as well as a pair of air passageways 36, 36′, which areconfigured to balance forces exerted between the forming pin 14 and thepin sleeve 16. While it is within the purview of the present inventionthat a pair of diametrically opposed air passageways can be employed,experience has shown that the use of three air passageways 34, 36, 36′,desirably acts to provide stable balancing forces between the formingpin and pin sleeve. By this arrangement, undesirable binding between thetooling components is desirably avoided. As will be recognized, morethan three air passageways can be provided between the forming pin andpin sleeve, with the desired effect being balancing of forces created byair pressure within the tooling assembly, thereby avoiding binding andundesirable wear.

As will be appreciated, the provision of air passageways 34, 36, 36′,defined between the forming pin and the pin sleeve, desirably avoids therequirement for additional internal components within the toolingassembly. Rather, the passageways can be provided by formingchannel-like regions at the interface of the forming pin and pin sleeve.The air passageways can be desirably formed without any significantreduction in the structural integrity of the tooling, and without resortto any reduction in the size of the coolant passages (not shown) withinthe tooling assembly.

In order to provide the desired distribution of pressurized air betweenthe plural air passageways, the tooling assembly includes at least onecircumferential channel 38, extending between the forming pin 14 and thepin sleeve 16, for joining the plurality of air passageways in fluidcommunication with each other. Circumferential channel 38 acts todistribute pressurized air introduced into the tooling assembly to theplural air passageways provided between the pin sleeve and forming pin,thus achieving the desired balancing of forces exerted between theforming pin and pin sleeve.

In accordance with the illustrated embodiment, it is presently preferredthat another circumferential channel 40 be provided in generally axiallyspaced relationship to channel 38. Channel 40 is also in fluidcommunication with a plurality of air passageways 34, 36, 36′, anddesirably functions as an accumulator to accumulate pressurized airprior to introduction of the air into a plastic closure being formed.

Pressurized air from channel 40 is directed into the mold cavity 22 by aplurality of smaller air passageways 42 which are spacedcircumferentially about the forming pin 14 generally between the formingpin and the distal end of the outer pin sleeve 16. Passageways 42 can beformed by flats defined by the forming pin 14, with a current embodimentincluding eight such passageways.

The specific configuration of the mold tooling assembly 10 of thepresent apparatus will, of course, be dependent upon the specificstructural features of the plastic closure C being molded. For manyapplications, it is desirable to provide the closure C withtamper-indicating capabilities, and to this end, the plastic closure istypically provided with at least one tamper-indicating element providedon the inside surface of the skirt portion of the closure. Suchtamper-indicating elements are diagrammatically illustrated in phantomline at E in FIG. 8, with these types of tamper-indicating elementstypically being provided in the form of one or more projections whichare configured to operatively engage the associated container duringclosure removal. Typically, a frangible connection is provided between alower portion of the closure skirt and the remainder of the skirt,whereby engagement of the one or more tamper-indicating elements withthe associated container effects fracture of the skirt portion, and thusreadily visibly discernable evidence that the closure has been partiallyor completely removed from the associated container.

In order to form closure C with one or more such tamper-indicatingelements E, the mold tooling assembly 10 is configured such that thecentral forming pin 14 and outer pin sleeve 16 are relatively movable,and define an annular forming surface 44 therebetween adjacent a freeedge of the skirt portion S of the plastic closure C. FIG. 5 illustratesforming pin 14 and outer pin sleeve 16 after such relative movementtherebetween, as would take place after removal of the molded closure Cfrom within female mold 20.

Notably, forming surface 44 not only provides a surface against whichthe one or more tamper-indicating elements E are formed, butadditionally cooperates with a mating annular surface at the distal endof the pin sleeve 16 such that the forming pin and pin sleeve acttogether to control flow of pressurized air into the molded closure asthe air moves out of air passageways 42. A throttling-like effect isachieved, as pressurized air is directed between the forming pin and thepin sleeve. It is presently preferred that this valve-like region not becompletely air tight, since this region desirably provides a vent pathfor air to leave the mold cavity 22 as the mold assembly is beingclosed, and plastic flows upwardly about the forming pin 14. Venting ofair during this portion of the molding cycle is especially preferred toavoid the formation of air bubbles or other voids in the molded plasticarticle.

Relative axial movement of the forming pin 14 and pin sleeve 16 may bemechanically effected, such as by cam-actuation, but in a typicalconstruction, the tooling is configured for relative movement which isinduced attendant to opening of the mold assembly by separation of thefemale mold 20 from the male mold assembly 12.

After the relative movement of forming pin 14 and pin sleeve 16,illustrated in FIG. 5 for facilitating removal of the tamper-indicatingelements of the plastic closure C, removal of the plastic closure fromthe forming pin is effected by “stripping” of the plastic closure fromthe forming pin, without relative rotation or “unthreading” of thethread formation or other retention element of the closure from thefeatures of the forming pin in which the thread formation is formed.Closure ejection is effected by relative movement of the forming pin 14and outer pin sleeve 16 relative to ejection sleeve 18. Again, suchrelative movement is typically effected by cam-actuation, such as byupward movement of the forming pin and pin sleeve relative to thevertically fixed ejection sleeve 18.

Heretofore, ejection of the plastic closure was effected by creation ofsufficient force against the free edge of the skirt portion of theclosure by ejection sleeve 18 so as to urge the thread formation of theclosure out of and off of the forming pin 14. This, of course, requiresthe closure to be sufficiently solidified as to avoid excessive bulgingor deformation of the skirt portion, particularly in the region of thetamper-indicating pilfer band. Additionally, the relatively large forcesto which the just-formed closure threads were typically subjected actedto limit forming speeds, since the threads needed to be sufficientlysolidified as to preclude unacceptable deformation as the closure wasforcibly stripped from the forming pin.

In accordance with the present invention, the direction of pressurizedair into the closure during the ejection phase of the molding cycle verysignificantly reduces the stresses to which the closure is subjected,thus reducing the level of solidification and strength that the closuremust exhibit during the stripping process. This, in turn, directlyresults in significantly increased operational speeds for thecompression molding apparatus.

In order to effectively pressurize the interior of the closure C, it iscontemplated that the closure be sealed, to a sufficient degree, at thefree edge of the closure skirt portion against the ejection sleeve 18.FIG. 6 illustrates the closure in this sealed disposition with respectto the ejection sleeve 18, with the annular forming surface 44 of theforming pin, and its cooperating mating surface at the free end of pinsleeve 16, having been opened to facilitate removal of the closuretamper-indicating elements.

Pressurized air is directed into the plastic closure from theaccumulator circumferential channel 40, through the plural airpassageways 42, and across annular forming surface 44. By thisarrangement, pressurized air is directed into the plastic closure in theregion between the thread formation T, or other retention element of theclosure, and the surface of the closure which engages the ejectionsleeve 18, typically the free edge of skirt portion S. Thecircumferential seal created between the free edge of the closure andthe ejection sleeve 18 is effective to permit the pressurized air beingdirected into the closure to act against the inside surface of theclosure skirt (as indicated by the arrows in FIG. 6) and thereby bulgeor “balloon” the closure as the closure is urged off of the forming pinby relative movement of the forming pin and the ejection sleeve 18.

Introduction of pressurized air into this region of the molded closureis particularly preferred, since it acts at the portion of the closurebetween the thread formation and the free edge of the closure tooutwardly bulge the portion of the closure positioned above (referringto the illustrated orientation) the thread formation. This is insignificant distinction from previous air ejection arrangements, inwhich air is directed into a closure between the thread formation (orother retention element) and the closure top wall portion. In suchprevious arrangements, the thread formation can undesirably act as aseal against flow of pressurized air against the entire inside surfaceof the skirt portion, particularly that region adjacent the free edge ofthe skirt at which outward bulging is most desired for reducing thestresses created on the closure threads during stripping from theforming pin.

Pressurized air is directed through the male mold assembly from theassociated rotary union during this portion of the molding cycle as theclosure is sealed against the ejection sleeve 18, with sufficient dwellcreated in the operation of the mold tooling to permit sufficientpressurization of the closure. In a typical application, pressurized airis delivered through the air supply system at a pressure of about 50psi.

FIG. 7 illustrates further internal pressurization of the closure C asthe closure is stripped from the forming pin 14 by the ejection sleeve18. As indicated by the arrows, air pressure within the closure actsagainst the inside surface of the skirt portion of the closure, as wellas against the inside surface of the top wall W of the molded closure.

The inside surface of the top wall of the closure will be momentarilypressurized as the closure is removed from the forming pin 14 asufficient amount as to permit the pressurized air being directed intothe closure to move around the peripheral bottom edge of the forming pin14. By breaking the natural vacuum which ordinarily is created betweenthe inside surface of the closure and the bottom surface of the formingpin, closures having flatter, more planar top walls can be formed.

As air pressurization acts to outwardly bulge the skirt portion of theclosure to facilitate disengagement of the thread formation T from theforming pin 14, the one or more tamper-indicating elements of theclosure are urged outwardly off of the forming surface 44 of the formingpin 14. In effect, a “radial” ejection force is created. This desirablyacts to reduce the stresses to which the tamper-indicating elements aresubjected during closure ejection, thus desirably resulting in enhancedstrength for such elements. Enhanced strength for such elements canfacilitate their desired mechanical interaction with an associatedcontainer for tamper-indication.

FIG. 8 illustrates completion of the ejection cycle with removal ofclosure C from the forming pin 14. The relative movement between theforming pin 14 and the ejection sleeve 18 has been completed, and theforming surface 44 of the forming pin again moved into cooperatingrelationship with the mating annular surface at the distal end of outerpin sleeve 16. At this portion of the molding cycle, air pressure beingdirected into the mold assembly from the associated rotary union isdiscontinued, thus preparing the mold assembly for the next mold cycle.

Thus, the present invention greatly facilitates high-speed manufactureof molded plastic closures. Internal pressurization of the moldedclosure during ejection greatly reduces the stresses to which theclosure is subjected as it is mechanically stripped from the associatedforming in, thus permitting significantly increased operating speeds,while at the same time reducing permanent deformation of the moldedclosure. Improved formation of tamper-indicating features is alsoachieved. Because the present apparatus is configured so as to directpressurized air between the forming pin and associated pin sleeve, thetypical coolant passages in the tooling can be sized as desired, withthe air passages further facilitating venting of the mold cavity as theclosure is formed.

The reduction in interference between the forming pin and the moldedclosure, and the resulting reduction in ejection forces, desirablyresults in reduced thread deformation, reduced bulging of thetamper-indicating band portion of the closure, and reduced external sidewall deformation at the thread locations. The high pressure airintroduced into the molded closure has the further benefit of reducingthe top panel concavity due to the reduction in the vacuum forcesgenerated during ejection, and provides a deformation which counteractsthe concave shrinkage of the top wall typically associated with thefinished closure. The reduction in molding cooling time results in asignificant decrease in the overall cycle time to form, cool, and ejectthe molded closure.

From the foregoing, numerous modifications and variations can beeffected without departing from the true spirit and scope of the novelconcept of the present invention. It is to be understood that nolimitation with respect to the specific embodiment illustrated herein isintended or should be inferred. The disclosure is intended to cover, bythe appended claims, all such modifications as fall within the scope ofthe claims.

1. An apparatus for molding a plastic closure having a top wall portionand an annular skirt portion, the apparatus comprising: a male moldassembly comprising a central forming pin, an outer pin sleeve withinwhich said forming pin is positioned, and disposed coaxially about saidforming pin and said outer pin sleeve, an ejector sleeve comprising: (i)a surface to sealingly engage a free end of said annular skirt portionof a closure molded upon said male mold assembly, said sealingengagement being characterized by its ability to maintain sufficientpressure in the closure during closure ejection to sustain a bulge inthe closure annular skirt; and (ii) means to engage a closure moldedupon said male mold assembly when moved axially relative to said moldassembly, thereby ejecting said closure from said male mold assembly;and a female mold which cooperates with said male mold assembly todefine a mold cavity in which to form said plastic closure, wherein saidmale mold assembly and said female mold are characterized further inthat they are axially moveable relative to each other and, said malemold assembly is further characterized in having at least one airpassageway in fluid communication with an inside surface of said skirtportion of a closure molded thereupon, said passageway being positionedto permit pressurized gas conveyed through said passageway to contact atleast a portion of said inside surface of said skirt portion.
 2. Anapparatus for molding a plastic closure in accordance with claim 1,including: a plurality of air passageways extending axially between saidcentral forming pin and said outer pin sleeve.
 3. An apparatus formolding a plastic closure in accordance with claim 2, including: atleast one circumferential channel extending between said forming pin andpin sleeve joining said plurality of air passageways in fluidcommunication.
 4. An apparatus for molding a plastic closure inaccordance with claim 1 wherein said male mold assembly is configured toform at least one retention element on the inside surface of said skirtportion of a closure molded thereupon.
 5. The apparatus of claim 4wherein at least one said air passageway is in fluid communication withat least a portion of the inside surface of said skirt residing betweensaid retention element and a free end of said skirt portion of a closuremolded upon the male mold assembly.
 6. The apparatus of claim 5 fittedto a compression molding apparatus and adjusted to eject a closuremolded upon said male mold assembly prior to complete solidification ofthe plastic comprising said closure.
 7. An apparatus for molding aplastic closure in accordance with claim 1, wherein: said centralforming pin and said outer pin sleeve are relatively movable and definean annular forming surface therebetween adjacent a free edge of saidskirt portion of said plastic closure, said skirt portion of saidplastic closure including at least one tamper indicating clement formedagainst said annular forming surface.
 8. An apparatus according to claim7 wherein said forming pin and said outer pin sleeve define cooperatingannular surfaces for controlling flow of pressurized air into saidmolded plastic closure.
 9. An apparatus for molding a plastic closure inaccordance with claim 8, wherein: said skirt portion of said plasticclosure includes at least one tamper-indicating element formed againstsaid annular surface of said central forming pin.
 10. An apparatus formolding a plastic closure in accordance with claim 8, wherein: saidcooperating annular surfaces of said central forming pin and said outerpin sleeve provide a vent path for air within said mold cavity duringmolding of said plastic closure.
 11. An apparatus for molding a plasticclosure in accordance with claim 8, wherein: said at least one airpassageway extends between said forming pin and said pin sleeve.
 12. Anapparatus for molding a plastic closure in accordance with claim 1,wherein: said central forming pin and said outer pin sleeve arerelatively movable and define cooperating annular surfaces forcontrolling flow of pressurized gas directed against said inside surfaceof said skirt portion of a closure molded thereupon.